24 Dec 2013

Alan Turing: codebreaker and imagineer hounded by the state

Paul Mason profiles the mathematician and computer scientist Alan Turing, who has been pardoned by the Queen today.

Alan Turing did not invent the computer. He imagined it. As a 24 year-old research student in 1936 he designed the “Turing Machine” – a conceptual binary machine using tape, storage and instructions. Then he imagined how you would programme it.

Daringly, he showed that once you could programme such a machine, then by re-programming it you could emulate all other computing machines. In a world where there were thousands of physical machines designed for specific uses, he insisted there would only ever need to be one kind of computer.

As you multi-task on your new tablet this festive season, or follow the GPS in your car, or take off into a computer-controlled airspace powered by an engine reporting performance data to its makers in real time – just remember, these things are possible because a man obsessed with logic and philosophical puzzles – not switches and circuits – put his mind to inventing them.

By the time war broke out Turing, building on the work of Polish mathematicians, had gone a long way towards understanding how to crack the Enigma machine – the coded typewriter at the heart of the Nazi war effort.

Reporting to the spy base at Bletchley Park the day after the second world war broke out, Turing set to work designing a massive calculator. Because the German codes changed constantly this calculator – known as the Bombe – would have to crack Enigma again and again. Turing’s mind was crucial to this operation. He reduced the machine’s task to a logical theorem: any system that can make mistakes must have order.

Cracking Enigma and AI

He drove the execution of the codebreaking work, which was painstaking and highly secret. And he personally supervised the breaking of the German naval Enigma machine, turning the tide in the U-boat war.

Then in 1943 he got on a boat to New York – braving U-boat attacks – to lead the British effort to forge intelligence collaboration with the US. There he discussed the possible design of thinking machines with Claude Shannon, the US mathematician who went on to found “information theory”. On arrival, Turing’s cover was so good that – lacking official letters explaining who he was – he was detained by the immigration service.

After the war, Turing worked on the early British computer projects, which were bound up with missile and atomic research. As engineers struggled with the circuitry, Turing worked on something more challenging: a theory of artificial intelligence. The “Turing Test” remains, 50 years on, the reference point for all discussions of how we can tell if a machine is “thinking”.


But Turing was openly gay – or at least as open as he could be in a society in which homosexuality was illegal. He’d had male lovers at Cambridge. He was open with his male lovers with colleagues at Manchester University, after the war.

There was, in the 1950s, an underground gay lifestyle but homosexuality was illegal. In 1952, when he reported his flat burgled, and the police realised he was living with a man, Turing and his lover were arrested and convicted of gross indecency. To avoid prison he accepted “chemical castration” – being injected with oestrogen.

Hounded for his homosexuality

His security clearance was revoked. This was the height of the Cold War, just after two Cambridge-educated British spies, Maclean and Burgess (who was also gay), defected to the USSR.

Turing travelled to France, Greece and Scandinavia, where the gay scene was more open. But as someone who had worked on the British atom bomb, a convicted criminal and with a similar profile to the escaped spy Burgess, he was under constant surveillance. When a Norwegian lover came to visit him, the police launched a manhunt across northern Britain to intercept him, fearing some intelligence breach.

He died, apparently by suicide with an apple impregnated with cyanide, in 1954.

Turing was driven to his death by a culture that had become paranoid about all dissent – and he was not even a dissenter.

His work at Bletchley Park probably shortened the war by two years. If you consider what those two years might have been like – with the Soviets in control of Europe, Britain starving because of the U-boat war, the Holocaust with two extra years to run, weapons of mass destruction available to both sides – you get a sense of the debt we owe to Turing.

As for his place in the history of computing: there were three or four others of that generation, drawn from physics and engineering, who stand alongside Turing in influence. But Turing made the crucial connection between logic, machines and the universal potential of “programming”. Turing – in modern parlance – was the imagineer.

A war hero and one of the 20th century’s greatest minds, he was hounded to his death by the security establishment. If today’s pardon represents justice, it has been a long time coming.

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2 reader comments

  1. Philip says:

    I realise the Establishment in the UK is stultified – but on earth has it taken so long?

  2. quietoaktree says:

    Is this Pardon really for Turing ?

    –or for GCHQ ?

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